It's not a common neeed, so there's no API to do that. You could look at the source code for `init_sims()` and mimic what it does to perform your unit-normalization of `syn1neg`. You can review the source in your own local gensim installation, or online:
(Note that the varied raw magnitudes in both `vectors` and `syn1neg` are a necessary part of the model's training state during training and may have some interpretive value for some applications, so don't clobber/replace those values unless you're done training and are sure you won't want the raw magnitudes.)
It's not inherently the case that the traditional word-vector (the 'input' or 'projection' vector in `vectors`) will become "close" to the negative-sampling-mode output-node-weights vector for that same word (in `syn1neg`) after "sufficient training".
- Gordon